The present invention relates to a photosensitive polyimide precursor. More particularly, the invention relates to a highly photosensitive polyimide precursor capable of giving a polyimide resin having a high heat resistance, as well as to a process for producing said photosensitive polyimide precursor.
Having performances as an electronic material such as heat resistance, insulating property, adhesion, etc., polyimide resins are used in the field of semi-conductor industry of the current age as a substitute for inorganic materials.
Among them, photosensitive polyimide resins are watched with a particular interest, because they enable to simplify the production process of semi-conductors to a great extent and they enable to make the pattern even, in addition to their characteristic properties as a polyimide resin. However, the existing photosensitive polyimide resins are not always satisfactory in the photosensitivity.
The present invention provides a photosensitive polyimide precursor which has a photosensitivity enough for the use as a starting material for production of semi-conductors, and enables to form a minute polyimide pattern with an excellent heat resistance.
The hitherto known polyimide type photosensitive resins are classified into two types.
One type is polyimide precursors having photosensitive groups on the side chains and the other is polyimides having photosensitive groups in the main chain.
The former polymers (polymers having photosensitive groups on the side chains) are proposed, for example; a polyimide precursor having a structural unit represented by the following formula is proposed in Japanese Patent Kokai (Laid open) No. 116,216/79. EQU --OC--R.sub.1 (CONHCOR.sub.3).sub.2 COHN--R--NH--
wherein R.sub.1 and R.sub.2 represent an aromatic cyclic group and R.sub.3 represents a group having double bond capable of dimerization or polymerization. These polymers partially lose the photosensitive components in the course of dehydration cyclization at high temperatures, and this results in a marked decrease in film weight, volume or thickness. In addition, they are unsatisfactory in photosensitivity. That is to say, they have various faults from the practical point of view.
On the other hand, the latter polymers (polymers having photosensitive groups in the main chain) are free from danger of losing the photosensitive components in the course of high temperature process. For example, an imide resin prepared by using a diamine represented by the following general formula[IV] as a diamine component is proposed in Japanese Patent Kokai (Laid-Open) No. 131,227/82, EQU H.sub.2 N--R.sub.1 --CH.dbd.CH--R.sub.2 --NH.sub.2 [IV]
wherein R.sub.1 and R.sub.2 each represent a divalent aromatic or aliphatic groups, and a polyamide-imide resin prepared by using a diamine represented by the following general formula [V] as a diamine component is proposed in Japanese Patent Kokai (Laid-Open) No. 145,216/84. ##STR3##
Both of these polymers are characterized in that they are soluble in organic solvents. However, they are both unsatisfactory in that the polymers proposed in Japanese Patent Kokai (Laid-Open) No. 131,227/82 have a low heat decomposition temperature of 310.degree.-380.degree. C. and a poor photosensitivity of about 5 J/cm.sup.2 and those proposed in Japanese Patent Kokai (Laid-Open) No. 145,216/84 have so poor a photosensitivity as worse than 3.5 J/cm.sup.2 even though their heat decompsoition temperature is 400.degree. C. or above.